Power system



K. SCHMIDT POWER SYSTEM June 24, 1930.

Filed March 17, 1928 (Des,

fat,

mvsmorr.' v Karl Sc midt.

Olin

ATTORNEY Patented June 24, 1930 UNITED STATES PATENT OFFICE KABL SCHMIDT, OF BERLIN-LICHTENRADE, GERMANY, ASSIGNOB TO C. LORENZ,

AKTIENGESELLSCHAFT,- OF BERLIN-TEMPELHOF, GERMANY POWER SYSTEM Application filed March' 17, 1928, Serial Noi This invention relates to a system of introducing an intermediate frequency into the power line for signaling and control purposes.

An object of this invention is to introduce an intermediate frequency into the power line in such a manner that a reaction on the intermediate frequency apparatus by the power frequency is prevented. 1 Another object of this invention is to provide means for introducing two or more intermediate frequencies into the same power An additional object of this invention is to provide a single apparatus such as a dynamo for introducing a large number of intermediate frequencies into the same power line.

In a preferred embodiment of my invention I have represented the means employed in the appended drawings, of which Fig. 1 is a system of introducing an intermediate frequency into the power line according to my invention,

Fig. 2 is a modified arrangement according to myinvention.

In electrical power networks it is often desirable to effect switching movements at distant points of the network, as for example, at consuming points from a generating station, substation, or the like. For this purpose, it has been proposed to use currents of an intermediate frequency which are superimposed upon the power line and which serve to actuate a relay at the distant point, as for example, a frequency relay. Thus, by employing several such currents of different frequencies, different distant control= ling movements may be effected. For instance, such distant control may serve to adjust electricity meters at the consuming polnts to different tariffs in accordance with the loading period of the power station, or they may serve to directly switch in or out distant consumers such as street lighting apparatus and the like. This invention has reference to all such arrangements where. a distant control or signalingv along power lines is required.

There are many difiiculties in superim- 262,461, and in Germany March 18, 1927.

posing the intermediate frequency currents upon the power line. The most important is that the intermediate frequency currents cannot be separated in the usual manner from the power frequency currents on account of the small difference in the freqency values. Furthermore it is only with great difliculty that the strong power frequency currents may be prevented from entering into the intermediate frequency apparatus. Hitherto, for this latter purpose blocking circuits containing condensers and making use of resonance phenomena have been employed. These condensers, however, are necessarily of very large dimensions, especial-' ly because of the high voltages generally in use today on power lines and in consideration of the relatively low frequencies involved. Therefore, the cost of the apparatus in question is increased to a considerable extent.

It is the object of the present invention to overcome the aforesaid disadvantages by providing means permitting to dispense with arrangements employing expensive condensers andmaking it possible to superimpose intermediate frequency signaling or controlling currents upon a power line in the most simple and easy manner.

According to this invention, the intermediate frequency current is superimposed upon the direct current exciting current of a synchronous machine which is connected to the power line in any desired manner. The intermediate frequency current is thus transferred from the exciter poles to the stator winding in a purely inductive manner and consequently upon the power line. A transfer of power currents from the line into the exciter winding carrying the intermediate frequency currents is thus readily prevented. For this purpose, for instance, an additional synchronous generator driven by a synchronous motor may be provided, or a synchronous motor running at no load, preferably one of those used for compensating'purposes may be employed. Furthermore, a synchronous alternator at a central station may also be employed for the purpose in question.

The invention is made clearer by the following description taken with reference to the accompanying drawings representing two examples of carrying it into practice.

Referring to Fig. 1, T is a transformer connected to an incoming power line, as for example, a 100 K. V. line. The secondary of this transformer carrying, for example, 6000 volts, includes an additional synchro- 'nous machine ZM whose rotor R is driven by a synchronous motor AM having its stator connected to the same network, as for example, as in the case shown, to the secondary of a second step-down transformer T The rotor winding of this additional synchronous machine ZM is supplied by a direct current source B, as for example, a battery or a generator, in series with an intermediate frequency generator MG. The direct current source, however, may be dispensed with.

Whenever the rotor R is running synchronously with the power frequency, no voltage will be produced in this rotor at the power frequency. The intermediate frequency Howing through the rotor winding will then be transmitted to the power line without any reaction of power frequency currents on the intermediate frequency apparatus.

Fig. 2 shows an arrangement employing a synchronous motor SM preferably running at no load, through the exciting winding of which there flows the intermediate frequency current in a manner similar to that of Fig. l.

The connections shown may be used in single phase or polyphase systems. For instance, a synchronous motor running at no load and serving for phase compensation, as it is very frequently employed on power networks, may be employed for the superimposition of the intermediary frequency currents upon the line in accordance with the present invention,

The intermediate frequency currents superimposed upon the power line may be employed for different purposes such as for signaling, or distant control, as is well known in the art. It will be seen that with a system as described, there will be produced two frequencies in the stator of the synchronous machine referred to hereinafter as side frequencies. When assuming a normal power requency of 50 cycles, both side frequencies will be obtained by addition and subtraction of the introduced intermediate frequency and the power frequency. For instance, if the intermediate frequency is 500 cycles, there will be produced in the armature, and therefore in the power line, two fre uencies, 550.

and 450 cycles respectively. explanation of this is that it is possible to decompose the 500 cycle exciting alternating field into two rotating fields running in opposite directions at the same speed. Hence, one of these rotating component fields is running 53 in the direction of the rotor speed and the other one is running opposite to the rotor speed. This latter corresponds to the 50 cycle frequency, so that the intermediate frequencies produced in the armature will have a frequency given by the sum and the difference of 500 and 50 cycles respectively.

Having described my invention, what I believe to be new and desire to secure and protect by Letters Patent of the United States is 1. In a power network of a definite frequency, a system for superimposing other frequencies on said network comprising a synchronous machine of the network frequency, an exciter winding for said synchro' nous machine, and means for introducing a second frequency to the exciter circuit of said machine.

2. In a power network of a definite frequency, a system for superimposing other frequencies on said network comprising a synchronous motor in said network, a generator driven by said motor, an exciting winding for said generator, and means for introducing an intermediate frequency into said exciting winding.

3. In a power network of a definite frequency including synchronous machines, a system for superimposing another frequency in said network comprising means for applying a second frequency to the exciter circuit of such synchronous machines.

4. In a power network of a definite frequency including synchronous generators, a system for superimposing another freuency in said network comprising means or applying a second frequency to the exciter circuit of such synchronous generators.

5. In a power network of a definite frequency, a system for superimposing other frequencies on said network comprising a synchronous machine of the network frequency, an exciter winding for said synchronous machine, and a generator of intermediate frequency to supply intermediate frequency current to the exciter winding of said s nehronous machine.

6. ii an electrical system carrying currents of definite frequency, means to introduce currents of different frequency into said system, said means comprising coupling elements moving with respect to each other at a speed synchronous with said definite frequency and means for applying a second frequency to one of said coupling elements.

7. In an electrical system carrying currents of definite frequency, means to introduce currents of different frequency into said system, said means comprising a synchronous machine having a rotating stator field corresponding to said first frequency, a rotor for said machine rotating synchronously with said field, a winding on said rotor and means to introduce currents of said second frequency into said windin 8. In a carrier current system for electrical alternating current power lines, means to introduce carrier current )f a frequency differing from-the power frequency into the power lines, the movement of one with respect to other of these elements being synchronous with said power frequency and means for applying a second frequency to one of said coupling elements.

9. In a carrier current system for electrical alternating current power lines, means to'introduce carrier current of a frequency differing from the power frequency into the power line comprising a synchronous machine having a rotating stator field corresponding to the power frequency, a rotor for said machine rotating synchronously with the power frequency and a winding on said rotor and means for introducing currents of said carrier frequency in said winding.

10. In combination with a system carrying alternating currents of definite frequency, means for introducing currents of a different frequency into said system, said signature.

means comprlsmg a coupling device associated with said system andhaving primary and secondary members, one of said members being constantly driven in respect to the other one of said members in synchronism with saiddefinite frequency thus preventing electric coupling for this frequency and means to supply current of frequency diflerent than said definite frequency to said coupling device.

11. In combination with an electrical alternating current power system of definite frequency, means for introducing carrier current of different frequency into said system, said means comprising a magnetlc coupling device having primary and secondary windings, means to produce a rotating magnetic field of said secondary winding in synchronism with said definite frequency, further means to drive said primary winding synchronously with said magnetic field to prevent coupling 1n respect to said definite frequency and means to introduce currents of said carrier frequency to the primary of said coupling device.

In testimony whereof I have afiixed my KARL SCHMIDT.

comprising coupling elements 

